Time to cut straight to the issue–the oil content of three of the most common drying oils. This information comes from the scholarly text Painting Materials.
- Walnut Oil–63-65%
- Sunflower Seed Oil–50%
- Linseed Oil–35-40%
And yet Linseed Oil is the most commonly used. Why?
To answer the question–tradition and availability. All these oils have a single molecular bond, which means they dry into a polymer when oxidized–i.e., when they are exposed to air (O2). Of the natural oils, only Tung oil has a double molecular bond, which makes it the most waterproof natural finish.
However, when heated for a long period of time, these natural oils form a double molecular bind, which means they dry faster, and become a durable polymerized surface. Heated linseed oil is often sold as “Danish” oil, which is a meaningless term that is used for all kinds of oil finishes.
Raw Linseed oil is a trendy diet item as well, sold as flaxseed oil. This has a very short shelf life, so treat it accordingly. You could just boil it and put it on your dining room table.
“Boiled” Linseed oil is just cheap Linseed oil with a bunch of toxic chemical dryers added. It makes a nice enough finish, and makes a very good base for an exterior paint, which is what I use it for. I don’t use it in any living area, but that could just be overly fastidious me.
Linseed oil , or Stand oil, sold to the art crowd (to make oil paint) is extremely high quality thickened oil, and is very expensive. No wonder a Van Gogh costs so much.
Sunflower Seed Oil
This is on my old Oak dining room table, which belonged to my grandmother, so the table has been around for awhile–she was born in the nineteenth century. This oil is cheap, durable, and dries fast. In fact, it is barely a fraction of the cost of a high quality Linseed oil. If you want to spend more for Linseed oil, just think that it is only money.
I loves me some Walnut oil. Expensive, yes, but it smells great and also tastes great. I keep mine in the frigernator to make it last longer. It also makes a superior base for a wax finish. It was also allegedly the secret ingredient for many of the old master painters
Making a Drying Oil
Any of these oils can be thickened using the old “stand” method of drying oils, which is leaving them out in the summer sun. In short, they stand out in the sun, which is quite intense here in the South. The danger is having the oil turn rancid, which could also explain the popularity of Linseed oil–less oil content means a lower chance of spoilage.
Which brings me to all the woodworking folks on the internet who insist that all natural oils turn rancid. These are drying oils, dopes. Olive oil isn’t, as with many cooking oils. The reason that the Louvre and the Uffizi galleries don’t stink is that the paintings were made with drying oils. More than a few were painted with tempera paint, which was often made with eggs as well. See how tough a dried egg yolk is sometimes.
Just because many people are saying something stupid doesn’t make it true. The great English woodworker Robin Wood (magnificent name, btw) pointed out that buying an expensive synthetic finish is illogical, when natural finishes are traditional, abundant, and less expensive–not to mention food safe and totally non-toxic. However, if someone admires the skull and cross-bones on the label, they should go for it. See who turns rancid first.